Barry Cameron

Evaluation of cold-water carbonates as a possible paleoclimatic indicator

Abstract The common belief currently shared by many geoscientists concerning the climatic interpretation of limestones is that a warm-water environment is essential. This concept is not necessarily true because the rate and extent of terrigenous sediment dilution, rather than water temperature, is the primary factor determining whether or not a limestone forms at nearshore or continental shelf depths. Because carbonate productivity is lowest in cold climates, however, CaCO3 abundance and the thickness of carbonate accumulations tend to be least at high latitudes. In this regard present-day continental shelves and beaches offer a poor model for comparing cold-water and warm-water carbonates because of the generally emergent continental tectonic framework, recent eustatic sea-level changes, and the presence of ice caps at the modern poles. Typically, the influence of climate on non-reef continental shelf and beach environments cannot be clearly distinguished by the presence or absence of major taxonomic groups. Faunal diversity and equitability are more sensitive in this regard. The absence of shelf-depth inorganic carbonate precipitates, micrite envelopes, and peloids may also point to the cold-water origin of a rock. Skeletal mineralogy and oxygen isotopes of certain unrecrystallized carbonates may be good paleoclimatic indicators; however, trace elements and physical-textural attributes of the carbonate fraction are probably temperature insensitive. Previous studies of high-latitude continental shelves have concentrated merely on the abundance of calcareous material and there is seemingly a disproportionate amount of information with respect to low-latitude carbonate studies. Further research on cold-water carbonates may open up new avenues for alternative paleoenvironmental and paleoclimatic interpretations.

Comparison between sieving and settling-tube determinations of sand sizes by using discriminant analysis

There is much controversy regarding the method that best measures the representative grain sizes used to calculate sediment statistics. Twenty-five sand-sized sediment samples were collected in barrier-island subenvironments and analyzed by a sieving technique and a settling-tube technique. On the basis of graphic sediment statistics as variables, discriminant analysis indicates that the more conventional sieving method correctly characterized 96 percent of the samples by subenvironments, while the settling-tube technique correctly characterized only 72 percent of the samples.

Preparation of Unconsolidated Sands for Microscopy Laboratory Exercises.

Microscopic examination of unconsolidated sands and coarse silts usually receives minimal attention in various sedimentology courses because of the difficulty of preparing adequate slides for study. Our technique for overcoming part of this problem is to impregnate small amounts of sandy sediment with a quick-curing resin. Once the sediment- resin plug is removed from a mold, it can be polished quickly for standard low magnification binocular (reflected light) microscopic studies. Using these easily made preparations, laboratory exercises with unconsolidated sands can be conducted efficiently for the determination of mineral composition, provenance, and grain roundness and sphericity in a manner that is comparable to the study of indurated sandstones in thin sections.

Microbial and Invertebrate Endolithic Assemblages from Late Cretaceous Belemnite Rostra: ABSTRACT

Thick-shelled oysters, belemnoids, and terebratuloids from the Upper Cretaceous Navesink and Mt. Laurel Formations of the New Jersey Coastal Plain show an abundant, diverse, and well-preserved assemblage of microbial and invertebrate borings. Macroscopic examination of invertebrate skeletons reveals large sponge, bivalve, gastropod, and annelid worm borings. Smaller borings in Belemnitella americana were resin-embedded and studied by SEM after acid dissolution of the rostrum skeleton. On the basis of morphology, size, and distribution patterns of the resin casts, at least a dozen borehole types can be recognized. The largest borings revealed by SEM (small microborings > 1 mm) include acrothoracian barnacles, clionid sponges, and phoronids(?). Mesoborings (100 to 1,000 µ) include bryozoans, clionid sponges, and some large unidentified branched algal(?) tubes. Most microborings cover the range of 1 to 100 µ and include branched tubes and bags of algal and fungal origin. The microborings are the most common and uniformly distributed members of the assemblage. End_of_Article - Last_Page 685------------

Recorrelation of Eocene-Miocene Boundary of Delaware Coastal Plain: GEOLOGIC NOTES

The Eocene-Miocene contact in the Delaware coastal plain should be moved down and placed below the pebbly, glauconitic sand of the uppermost Piney Point Formation (Jacksonian age). The uppermost part of the Piney Point Formation (glauconitic greensand), which is pebbly, lacks a characteristic late Eocene fauna and contains middle Miocene Foraminifera, unquestionably making this pebbly sand Miocene in age. Thus, a new correlation can be drawn on the basis of the microfossils, rather than on the green color due to the presence of glauconite.

Peel preparation box

The use of an internally illuminated wooden box with a plate glass top for making acetate peels is described. The plate glass provides a uniformly smooth, flat surface which inhibits air bubble formation even with relatively large specimens. A mirror on the bottom of the box is used to immediately observe the quality of the peel.